The present invention relates to a knife and apparatus for clamping a knife in a wood chipper, such as a disc, drum or conical head chipper for use in the commercial processing of logs.
In wood chipping apparatus used in the forest products industry, a rotating member is provided for receiving replaceable knives for cutting chips from the log. Each knife is typically clamped to the rotating member between an outer clamping member and an inner clamping member or counterknife, wherein the knife and counterknife together form a surface against which the log is forced to remove chips from the log. The chips themselves have commercial value, and their removal shapes the log into lumber and finishes its surface. The clamping members essentially form a cassette for the knife, although the entire cassette is often referred to in the trade as a knife. Herein, the term “knife” is used to refer to the blade that is clamped between the outer and inner clamping members.
The spacing between the outer and inner clamping members is adjustable for loading the knife into the apparatus, or unloading the knife from the apparatus, such as for replacing the knife or turning the knife end-to-end to position an alternative knife edge in the chipper. A preferred mechanism for adjusting the spacing between an outer clamping member an inner clamping member is described in U.S. Pat. No. 5,979,522, also incorporated herein by reference in its entirety.
As one example of a wood chipping apparatus, a chipper disc typically spins in a vertical plane. A number of identical knives are spaced around the periphery of the disc. The knives are elongate, and their elongate axes are oriented along radial lines passing approximately through the center of the disc, the axis of each knife becoming horizontal at respective 9:00 and 3:00 positions of the disc. When unclamped, the knives are typically unrestrained from sliding along these radial lines, so it is preferable to unclamp the knives when they are at least approximately in one of these two level positions.
A shroud is typically provided that covers the disc to retain chips and to shield personnel, the shroud including a closeable opening in a predetermined angular position of rotation of the disc, to provide access to a knife that has become aligned therewith. The position of the opening is selected so that the heavy and sharp knife will not slip forwardly out of the apparatus when it is unclamped; however, even so, the knife remains free to slip backwardly into the apparatus and still presents some risk of injury or damage. Such considerations are important as well to other types of wood chippers, such as the drum and conical head chippers.
Accordingly, there is a need for a knife and apparatus for clamping the knife in a chipping apparatus that provides for more safely and securely preventing movement of an unclamped knife along a line of slippage extending into and out of the apparatus.